The present invention relates to aqueous dispersions containing modified polyolefin as their principal constituents, to a process for the production thereof and to the use thereof for the surface modification of solids, in particular for sizing glass fibers.
It is known that the properties of composites made from glass fibers and polymers are to a great extent influenced by the shear strength between the glass fibers and the polymers surrounding the glass fibers, the so-called matrix polymers. The task of the glass fiber size is to create this adhesion between the glass fibers and the matrix polymer, and moreover to ensure the production and processing properties of the glass fibers. The sizes used are compositions prepared from water, polymeric binders (so-called film formers), coupling agents, lubricants, anti-static agents and further auxiliary substances, wherein the formulations of the sizes must be optimized for the particular polymer matrix. Generally, the binders used are organic, water-dispersible or soluble polyvinyl acetate, polyester, polyester epoxide, polyurethane, polyacrylate, polyolefin resins or mixtures thereof.
It is in principle highly problematic to reinforce polyolefins with glass fibers due to the chemical inertness and low polarity of polyolefins. Glass fibers have relatively high surface polarity and are thus largely incompatible with polyolefins. Consequently, polyolefin dispersions (BE 750 649, BE 807 979 and U.S. Pat. No. 3,480,580) are virtually exclusively used as the film formers for glass fibers suitable for polyolefins. Other film formers, for example containing polyurethane, vinyl acetate or epoxide are, in contrast, incompatible with polyolefins and are unsuitable as they prevent any bond between the fiber and matrix. In these cases, the composites produced from glass fibers and polyolefins exhibit deficient mechanical properties, such as, for example, tensile and flexural strength or impact strength.
There is, however, demand from the market for glass fibers which are also suitable for reinforcing polyolefins and which, in comparison with the prior art, offer improved properties, in particular improved tensile and flexural strength, of the polyolefin matrix.
The object of the invention is thus to provide a dispersion which is suitable for coating the surface of solids, in particular for sizing glass fibers, which dispersion increases compatibility between the surface of the solid and the matrix olefin and so improves adhesive properties.